It has always been a goal to increase the energy transfer efficiency, within practical financial limits and operating specifications, of systems which involve heat transfer. Examples of such systems include: steam boilers which typically burn fossil fuel to convert water to steam for use in heating, cooling, process manufacturing, or the driving of turbines to produce electricity; oil refinery furnaces which burn fossil fuel to heat crude oil to produce various petroleum products; and food processing systems which use fossil fuel to heat vegetable oil to produce a variety of products. It is a goal of such systems, within practical financial limits and operating specifications, to transfer as much of the heat value of the fuel as possible to the substance or material being heated. Many of these systems burn millions of dollars of fuel per year, and thus small changes in efficiency can translate into large monetary savings.
The standard basis for measuring efficiency of boilers is the ASME power test code 4.1. This test code employs two measurement methods: input-output, and heat-loss. These methods are theoretically equivalent, and are considered to be measures of the effectiveness of the boiler in extracting the available heat energy of the fuel. In the input-output method, the efficiency is measured as the amount of heat absorbed by the water and steam, compared to the energy input of the fuel.
This method requires the accurate measurement of fuel input. Also, accurate data must be available on steam pressure, steam temperature, steam flow, feed water temperature, stack temperature, and air temperature. The heat-loss method subtracts individual energy losses from 100% to obtain percent efficiency. The losses measured include heat loss due to dry gas, heat loss due to moisture in the fuel, heat loss due to water from the combustion of hydrogen, heat loss due to combustibles in coal refuse, heat loss due to radiation, and other unmeasured losses. The major contributor to the heat loss is the flue gas.
Although these calculations can be accurate, they require the testing party to gather a large amount of data, and thus are cumbersome to perform. In addition, these tests are performed under a range of operating variables that may comprise only a small percent of the actual range of operating variables the equipment operates under. The input-output method demands precision instruments to measure such items as steam pressure, steam temperature, steam flow, fuel input, feed water temperature, stack temperature, and air temperature. Furthermore, a steam plant may not be able to support testing for long periods of time because of practical considerations such as the demand of steam required to produce required electricity.
In the above described methods, accurately measuring the change in efficiency resulting from the introduction of a device, system, or operational method to the thermal transfer system would be difficult to quantify, as only a small range of operating variables may be observed before and after such introduction. Additionally, significant changes in operating variables such as a high wind velocity may be present before the introduction, but not present after the introduction, thereby affecting the objective of a controlled comparison. Additionally, operating variables have within themselves attributes that affect other operating variables, thereby creating an interrelationship that cannot be expressed under the above methods. An example of this is barometric pressure. At very low barometric pressures, less air is available to mix with the fuel. However, this may be offset by high winds that can occur at low pressures: the high winds at the stack can pull more volume of this low density air into the system's burner.